should be used. The value in os.environ will include a "s~" prefix for applications using the HR datastore and, by default, "dev~" on the development server. (os.environ should also be avoided entirely on App Engine anyway, since when concurrency support is added with the Python 2.7 runtime, use of os.environ won't be threadsafe and will allow data to leak from one request to another, although obviously the application ID itself would be the same for multiple requests to the same application at the same time...)